1. Field of the Invention
The present invention relates to optical apparatuses such as a television lens and a video lens, and, more particularly to an optical apparatus having an auto focus function.
2. Description of the Related Art
Conventionally, various proposals have been made as an auto focus (AF) technique in image taking apparatuses such as a camera and a video camera. For example, light beams from an object that have passed different exit pupil regions of a shooting lens are imaged on a pair of line sensors and a relative position displacement amount of a pair of image signals obtained by photoelectrically converting object images is calculated. An automatic focusing method for calculating a defocus amount of the object on the basis of the displacement amount and performing driving of the shooting lens is well known.
In image taking of moving images, it is necessary to control the position of a focus lens to constantly and automatically perform focusing.
Japanese Patent Application Laid-Open No. H04-217237 discloses a method of predicting, when it is temporarily impossible to perform focus detection, a position where an object is going to based on the moving speed of the object in the past and maintaining an in-focus state.
Japanese Patent Application Laid-Open No. H08-101337 discloses a method of adaptively switching lens driving according to a focus detection in order to obtain an in-focus state.
It is necessary to provide, in order to constantly maintain an in-focus state with respect to an object moving at high speed, plural focus detection systems to continue to capture the target object during taking moving images.
However, the prior arts disclosed in Japanese Patent Application Laid-Open No. H04-217237 and Japanese Patent Application Laid-Open No. H08-101337 do not cope with movement and a change in the object during taking the moving images and do not take into account an increase in processing time due to the provision of the plural focus detection systems and the influence of the prolonged processing time on the in-focus state. Therefore, it is difficult to maintain the in-focus state.